This invention relates to organosilicone compositions and processes and more particularly to a process for the stabilization of hexamethylcyclotrisiloxane and the stabilized compositions resulting therefrom.
Hexamethylcyclotrisiloxane (CH.sub.3).sub.2 SiO).sub.3 is a useful intermediate in the preparation of higher molecular weight poly(alkylsiloxane) fluids and gums which in turn have a wide variety of well-known uses, such as, for example, caulking and molding compositions.
Hexamethylcyclotrisiloxane, a solid at room temperature (m.p. 64.degree. C), is a considerably unstable material and prolonged standing and/or storage of the material, either in solid or molten form, results in spontaneous polymerization to undesirable high viscosity materials. Because of its use as an intermediate for subsequent reaction, hexamethylcyclotrisiloxane is generally stored, mostly for convenience purposes, in the molten state, i.e., maintained at a temperature above about 64.degree. C, its melting point, and below about 134.degree. C, its boiling point. The spontaneous polymerization to high viscosity materials occurs at even a faster rate when the material is stored in the molten state.
Although it is not known for certain, it is believed that the spontaneous polymerization which occurs in unstabilized hexamethylcyclotrisiloxane is caused by acidic impurities and/or ionic chloride impurities which are generally present as a result of its method of preparation. Attempts to preven the spontaneous polymerization resulting from these impurities using basic materials such as sodium bicarbonate, have not adequately stabilized the material. That is, it has been found that in the presence of sodium bicarbonate the spontaneous polymerization of the hexamethylcyclotrisiloxane proceeds at a reduced rate but is insufficient to provide adequate storage stability over an extended period.
Because of its instability, hexamethylcyclotrisiloxane is presently not stored for any length of time but generally, out of necessity, must be reacted to higher viscosity material almost immediately after its preparation.
Thus, as a result of the large quantities of hexamethylcyclotrisiloxane manufactured each year, a need has developed for a method to stabilize it, primarily to allow the material to be adequately stored without the loss of large quantities.